Hallo.
On 05.06.20 13:07, Koen Zandberg wrote:
Hello
On 03-06-2020 20:18, Stefan Schmidt wrote:
Hello.
Happy to see that we finally have the critical mass to get this moved
forward. :-)
Here is my take on what I think needs to be done.
On a first review I found nothing wrong with the design. It needs
further extending and flexibility in my opinion, though.
I would suggest using USB bulk endpoints for both the tx and rx paths.
An interrupt IN endpoint might be useful for events from the radio back
to the host such as ack information from a transmit. This way we can
keep the control messages to configuration only. This is similar to how
USB ethernet devices are using different USB endpoints. I also see
issues with transferring large 802.15.4g frames over control endpoints.
Something similar like CDC-ECM would be my preference here: Split the
frame in multiple bulk transfers and detect the end of the frame by a
transfer size not equal to the endpoint size.
That sounds fine to me. Adrei, what do you think about this change?
o Add a GET_EXTENDED_ADDR command to receive the extended address
provided by the transceiver itself, or firmware in some way.
+1
o Adding a GET_CAPABILITIES command to query device capabilities
during init to enable and set needed ieee802154_ops based on the
device. Given that we aim to support as many transceivers as possible
we can't rely on static device knowledge to configure wpanusb correctly.
Does it make sense to include also a "protocol" version here, to allow
extending the feature set of the driver later without causing
compatibility issues between the firmware and the kernel?
I was hoping that we could cover what we need with the current spec and
we could just add more capability flags for new things. We could got the
full way to have a protocol version during the init as well.
o Add opcode for set_lbt in USB spec
This requires some clarification for me how the radio should be
configured. Is this just a CSMA/CCA switch?
From what I have seen this listen before talk is often (always?) a
hardware feature of sub GHz (where its needed) transceivers. I would
assume this just makes sure we pass the config from linux stack through
the driver to the firmware.
o Add opcode for set_frame_retries USB spec. (If a transceiver does
not support AutoACK in hardware do Zephyr and RIOT support a software
fallback to handle AutoACK?)
This can be implemented in RIOT. I don't think there is something in
place at the moment, most of our radios support this in hardware, but I
see no technical reason why not to support this.
Good
o How are we going to handle transceiver which allow MTUs > 127? Not a
high priority as the kernel part does not support this either right now.
There is some preliminary support for 802.15.4g radios in RIOT. I know
some developers that would prefer not to have to have the MTU limited to
127 bytes :)
While we do not support this in the Linux stack yet, we should still
make sure the spec here is capable of supporting this.
o Do Zephyr or RIOT expose additional functionality we should support
here?
o Koen, you offered to look into implementing the firmware support for
the USB spec in RIOT. Does the spec fit what RIOT has as abstraction
for ieee802154?
Yes, implementing configuration settings as USB control messages makes
glueing them to the radio abstraction layer very easy. For now RIOT has
configuration for:
- reading and writing channel/page settings
- read/write to addresses, both long and short
- PAN ID
- TX power settings
- reading the max PSDU size
Hmm, we do not have that. But getting the info from the firmware would
be useful.
- Ack config settings
- CCA and CSMA configuration, enabling/disabling, retries and backoff
exponent (max/min)
- CCA threshold and mode
Is there a way to the device in promiscuous mode?
Furthermore, it is possible to get frame metadata such as the received
signal strength and the number of retries required for the frame
Currently the spec only covers LQI, but getting extra stats on the
reliability could bring in some extra benefit for routing decisions.
transmit. All these settings depend a bit on the radio hardware features
of course, but thats what we have the GET_CAPABILITIES for.
Yes, exactly, with the capabilities we get during init from the firmware
it can be signalled what it supports and we would enable the needed
device ops for the Linux stack ased on this.
regards
Stefan Schmidt
